The present invention relates to chord detection devices which detect a chord on the basis of performance data generated in response to performance on a keyboard musical instrument or the like.
In automatic bass chord performance and other types of automatic performances, automatic accompaniment tones can be generated in accordance with chords actually performed on a keyboard. To this end, it has been conventional to detect the roots and types of performed chords. For instance, note data are input which correspond to performance data produced by manual performance (key depression) on a keyboard of an electronic musical instrument, i.e., which correspond to one or more depressed keys, and the roots and types of such performed chords are detected on the basis of combination of the input note data corresponding to the depressed keys (depressed key pattern). In accordance with a typical example of the conventionally known chord detecting approaches, each time a key depression event has occurred, detection of a chord is attempted on the basis of a combination of note data corresponding to all then-depressed keys on a chord performing keyboard. However, this prior chord detecting approach is deficient in that, even when the player believes that he could simultaneously depress plural keys for a desired chord, there would undesirably be caused an appreciable variation in the actual key depression event occurrence time and that detection noise would often result from temporary chord detection errors caused by mistouching of keys.
To solve the above-mentioned problems, another chord detecting approach is proposed, in accordance with which a particular time point when a first key depression event (new key-on event) occurs from a state where all keys are released on a chord performing keyboard is designated as a trigger point, and a chord is detected on the basis of a note data combination pattern relative to key depression events having occurred within a predetermined period of time from the trigger point. This approach can ignore variation in key depression event time and mistouched key depression within a predetermined period and hence effectively enhance the chord detection accuracy. However, with this chord detecting approach, chord detection is allowed only after all the keys have been placed in the released state. Thus, in changing chords during a performance, the player always must make a key release operation to place all the keys in the released state prior to initiating key depression for a desired chord. This would considerably limit the freedom of the chord performance operation while making the operation very troublesome and could never allow chords to be changed in a legato-like manner.
Further, Japanese Patent Laid-open Publication No. SHO 61-289394 discloses another chord detecting approach, where a chord detection operation is made, for a predetermined period (period corresponding to a sixteenth note length, for example), periodically for each predetermined beat timing of automatic performance tempo (for each quarter note timing, for example). According to the disclosed approach, if depressed key notes vary during the given period, it is permitted to make chord detection in response to the variation; otherwise, no chord detection is made at all. With this approach, because chord detection is made on the basis of combination of depressed key notes generated for a predetermined period immediately after predetermined beat timing, no chord detection error would result from mistouched keys at other times; however, if some of component keys of a preceding chord has not been completely released at the beginning of the beat timing, it is possible that misdetection of chord results.